THORAX, LEGS, AND WINGS. 
43 
oscillation of its wings, which can be done, Marey 
says, by moving the abdomen so as to displace the 
centre of gravity ; so that the insect can, according to 
its wishes, increase the rapidity of its forward flight, 
lessen the speed acquired, retrograde, dart towards the 
side, or ascend and descend. 
It is easily seen that when a bee flying at full 
speed stops upon a flower, it directs the plane of 
oscillation of the wings backwards with considerable 
force. 
Marey was able to demonstrate, by means of 
models, this theory of flight in insects, and by the 
^ graphic method ’ he was able to show that the two 
wings act simultaneously, and that both perform the 
same number of movements. 
This was done by the graphic method in the fol- 
lowing manner : — A sheet of paper, blackened by the 
smoke of a wax candle, is stretched upon a cylinder, 
which revolves at the rate of one turn in a second and 
a half The insect is so held that one of its wings 
brushes against the blackened paper at every move- 
ment. Each of these contacts removes a portion of 
black on the paper, and as the cylinder revolves, new 
points present themselves continually to the wing of 
the insect. Thus regular marks at certain distances 
are obtained. As the cylinder revolves once in a 
second and a half, it is easy to see how many strokes 
of the wing are marked on the circumference ; but it 
is sometimes convenient to use a chronographic tuning 
fork provided with a fine point, which grazes the paper, 
and to register near the figure traced by the insect the 
vibrations which the style makes. 
